It is known to have communications networks having switching matrices at nodes. In some cases a node can be a hybrid node having two switching matrices operable using different protocols for different technologies, with internal links between the switching matrices. In some cases a control plane is used to generate and pass control messages between the nodes. A well known example of a type of control plane for controlling communications networks is Generalized MPLS (GMPLS) which extends MPLS (multiple protocol label switched) to handle multiple switching technologies, designated as follows: PSC (packet switch capable), L2SC (Layer-2 switch capable), TDM capable, LSC (lambda switch capable), and FSC (fiber switch capable), as stated in ref [1].
Most of the initial efforts to utilize GMPLS have been related to environments hosting devices with a single switching capability so that the resulting networks are composed by different layers and different technologies, which are called regions. Those networks are called Multi-Layer and Multi-Region Networks (MLN/MRN).
Future networks are going to integrate as much as possible the control of layers and regions, in order to optimize the exploitation of all network resources and characteristics. Therefore, network suppliers and network operators are facing new issues concerning the integration of different technologies and switching capabilities in single network devices, called hybrid nodes (i.e. nodes that can switch traffic at different layers which implies different protocols, for example at both electrical and optical layers).
By extending MPLS to support multiple switching technologies, GMPLS provides a comprehensive framework for the control of a multi-layered network of either a single switching technology or multiple switching technologies, but the integration of layers and technologies in hybrid nodes is challenging and a set of issues must be still addressed.
GMPLS-TE protocols and procedure described in IETF RFCs are quite stable concerning nodes with single switching capability, while a set of drafts, mostly from CCAMP group, are addressing the issues related to MLN/MRN networks and hybrid nodes.
In a MLN/MRN networks, the interaction between layers and regions is a key issue especially if these interactions are integrated in a single hybrid network element. This kind of element is a multi-switching-type-capable one that can terminate data links with different switching capabilities, where the data links are connected to the node by the same interface. So, it advertises a single TE link containing more than one ISCD each with a different ISC value. For example, a node may terminate PSC (packet switch capable) and TDM data links and interconnect those external data links via internal links. The external interfaces connected to the node have both PSC and TDM capabilities.
TE link advertisements issued by a hybrid node may need to provide information about the node's internal adjustment capabilities between the switching technologies supported. The term “adjustment” refers to the property of a hybrid node to interconnect the different switching capabilities that it provides through its external interfaces. The information about the adjustment capabilities of the nodes in the network allows the path computation process to select an end-to-end multi-layer or multi-region path that includes links with different switching capabilities joined by nodes that can adapt (i.e., adjust) the signal between the links.
The GMPLS control plane for hybrid node composed by heterogeneous switching capability (e.g. PSC and LSC) defines some information regarding internal link of the hybrid nodes that connect PSC and LSC). IETF proposed the Interface Adaptation Capability Descriptor (IACD) TLV (Type Length Value) in order to describe the internal links of a generic hybrid node. This object contains generic information, but without the detail typically needed for path computation.